Multi-stage carburetor



H. A. CARLSON ET AL 2,718,387

MULTI-STAGE CARBURETOR Sept. 20, 1955 Filed March 27, 1955 5Sheets-Sheet 1 6 m g a l U i I L( Ill Inn INVENTORS HAROLD A.CARLSONOLIN J. EICKMANN ATTORNEY Sept. 20, 1955 H. A. CARLSON ET AL 2,718,387

mumpsmcs CARBURETOR Filed March 27, 1953 5 Sheets-Sheet 2 Q m z\ m N N Mw HAROLD A. CARLSON OLIN J. EICKMANN ATTORNEY Sept. 20, 1955 H. A.CARLSON ET AL 2,718,387

MULTI-STAGE CARBURETOR Filed March 27, 1955 5 Sheets-Sheet 3 FIG.3.

FIG.5.

INVENTORS HAROLD A. CARLSON OLIN J. EICKMANN ATTORNEY Sept. 20, 1955Filed March 27, 1953 H. A. CARLSON ET AL 2,718,387

MULTL-STAGEZ CARBURETOR 5 Sheets-Sheet 4 INVENTORS HAROLD A. CARLSONOLIN J. EICKMANN BY W ATTORNEY Sept. 20, 1955 H. A. CARLSON ET AL2,718,387

MULTI-STAGE CARBURETOR Filed March 2'7, 1953 5 Sheets-Sheet 5 FIG.6Q

ATTORNEY United States Patent MULTI-STAGE CAREURETOR Harold A. Carlson,Brentwood, and Olin I. lEickmann,

Normandy, Mo, assignors to Carter Carburetor Corporation, St. Louis,Mo., a corporation of Delaware Application March 27, 1953, erial No.345,048

18 Claims. (Cl. 261-23) This invention relates to multi-barrel orinulti-stage carburetor systems for internal combustion engines. .foreparticularly, the invention relates to a novel combination of a fuelsupply and a new fuel nozzle system for such carburetors whicheliminates the necessity .of two separate fuel bowls and of fourseparate nozzle systems.

The invention is shown applied to the type of carburetor disclosed inthe application of Carlson and Moseley, Ser. No. 263,291, filed December26, 1951. Briefly, this prior application shows a multi-barrel,multi-stage carburetor with four barrels and four separate floatcharnbars, which chambers are connected in pairs to form two fuel bowls,each supplying fuel to two individual fuel nozzle systems.

The performance of carburetors with multiple fuel bowls and nozzlesystems is not wholly satisfactory be cause they cannot be readilycalibrated for changes in acceleration, cornering, braking, orinclination of the vehicle. Such changes can produce an unevendistribution of fuel with its accompanying disadvantages in engineperformance. Furthermore, the transition point which occurs when thesecondary stages go into action is very pronounced, and is regarded, forthat reason, as undesirable.

in the present invention, two fioat chambers are interconnected by arestricted passage to form a single fuel bowl. This bowl supplies fuelto two separate fuel nozzle systems of novel design-one for each pair ofprimary and secondary stages of the multi-barrel, multi-stagecarburetor. The location of the point of supply for each nozzle systemis adjacent one sideof the fuel bowl, preferably from a zone located inthe restricted passage connecting the float chambers. Each fuel systemhas a conventionally arranged low-speed nozzle or idling ports suppliedwith fuel through passages connecting with a main inclined fuel passagefrom the point of supply within the fuel bowl. The main or high-speedprimary and secondary nozzles are in a tube extending transversely ofthe primary and secondary stage barrels. connects with the inclined mainfuel passage from the fuel bowl. The junction between the tube and thepassage forms a single control point for both primary and secondarystage fuel nozzles, and this control point is pun posely locatedadjacent the volumetric center of the fuel bowl above the liquid level.Each fuel nozzle has one or more air bleeds at a point in a zonepressure-sensitive to throttle positions.

The combination of a single fuel bowl with twofuel nozzle systems hasbeen found to avoid unequal distribution of fuel, and its disadvantages.This is due to the proximity of the fuel supply for each fuel nozzlesystem, and to the feature of having a single control point for eachpair of main or high-speed nozzles. Because of the single control point,the amount of lift from the fuel bowl to each primary and secondarystage main nozzle is identical under the conditions above mentionedwhich occur due to accelerations or inclination of the vehicle.Furthermore, the interconnecting air bleeds provide a smooth transitionfrom primary to secondary stage by enriching This tube, in turn,

'1 263,291, filed December 26,

the mixture in the primary stage to compensate for the additional airadmitted through the secondary stage before the secondary stage fuelnozzle begins to function.

The accompanying drawings illustrate two forms of the instant invention.

Fig. l is a top plan view of a carburetor according to the presentinvention.

Fig. 2 is a vertical front elevational view of the carburetor with partsbroken away to show the adjacent points of fuel supply to the fuelnozzle systems within the fuel bowl.

Fig. 3 is a side elevational view of the carburetor with parts brokenaway to illustrate a float chamber and its float control mechanism.

Fig. 4 is a vertical longitudinal section through the carburetor.

Fig. 5 is a detail view of the choke valve-operated mechanism forlocking out the action of the throttles for the secondary stages.

Fig. 6 is a longitudinal section illustrating a modification of thepresent invention.

Fig. 7 is a diagrammatic view illustrating the lack of effect of changesin inclination of the vehicle on the relation between the fuel level inthe fuel bowl and the control point for the fuel nozzle.

The drawings illustrate a four-barrel downdraft carburetor with a bodyit). As shown in Fig. 1, this body includes two forward or primary stagemixture conduits ill and 12, and two rear or secondary stage mixtureconduits l3 and 14. These conduits are arranged in symmetrical relationin a compact group, and are supplied with air through arectangular-shaped air horn structure 15 provided with a transversepartition 16. At the forward side of the partition is journaled achokeshaft l7 mounting an unbalanced choke valve 18 (see Fig. 4-). Thechokeshaft is controlled by any suitable automatic choke controlmechanism within the housing 19 in Fig. 2. Extending across both primaryand secondary mixture conduits are throttle shafts 20 and 21 mountingthrottle valves 22 and 23. Each pair of primary throttles 22 moves as aunit. Likewise, each pair of secondary throttles 23 moves as a unit. Theprimary conduits may be connected by pressure-equalizing passages, andthe secondary conduits may be likewise connected, if desired. A flange26 surrounding the lower end of the conduits is provided for attachingthe carburetor to the usual engine intake manifold.

Referring to Figs. 2 andS, the primary throttle shaft 2 9 has aprojection onwhich is rigidly mounted a throttle-operating arm 27 havinga hole 23 for attachment to the usual accelerator linkage. The throttlearm carries an adjusting screw 29 for engaging a fast idle cam 34pivoted as at 31 to the carburetor body. The cam is connected by atorsion spring 32 to a concentrically pivoted loose lever 33, which, inturn, is connected by means of a link 34 to an arm 35 rigid with theprojecting extremity of choke valve shaft 17, which is located oppositesaid housing 19. A small disk 36 is rigid with the adjacent projectingextremity of a secondary throttle shaft 21, and has a radial lug 36a.Also loosely mounted with respect to the pivot element Tall is aneccentrically weighted stop lever 37 provided with a finger 33 which isnormally maintained by its own weight in position to interfere andengage with lug Sea on the secondary throttle shaft 21 when the chokevalve is closed. This lock mechanism is the same as that shown inctr-pending application Ser. No. 1951, by Carlson and Moseley. It isexplained therein that lug 39, which is integral with lever 33, willengage eccentrically weighted lever 37 as the choke valve moves towardopening position, thereby shifting the lever 37 to unlock the secondarythrottles 23 by its disengagement with the lug 36a.

The mechanism for operating the primary and secondary throttles in asequential manner is shown in Fig. 3, and this mechanism comprises asmall lever 100 fixed with primary throttle shaft 20, which lever isformed with radial and angularly extending lugs 101 and 102. A lever 103is rotatably mounted on throttle shaft inward of lever 100, and has afinger 104 connected by a coil tension spring 105 to the finger 101 ofthe operating lever 100. Spring 105 normally maintains a second integralfinger 102 in engagement with lug 106. Lever 103 has a second angularlug 107 mounted thereon for a purpose to be later described. Alsorotatably mounted on the throttle shaft is a third lever 108 inwardly offixed lever 100 and lever 103. This lever is connected by a link 109toan arm 110 rigidly secured with the adjacent projecting extremity ofsecondary throttle shaft 21. Arm 110 may be biased in acounter-clockwise direction by a suitable torsion spring 120 or thelike. In operation, counterclockwise movement of the shaft 20 to openthe primary throttles 22 moves lever 100, and lever 103 is likewiserotated through spring connection 105 until radial lug 107 engages ashoulder 113 on third lever 108, whereupon the three levers rotate as aunit, causing opening of the secondary throttles 23 by link 109 and arm110. Because of the lost motion connection between lug 107 and shoulder113, primary throttles 22 are in a partially opened position beforeengagement between lug 107 and shoulder 113 causes initial movement ofthe secondary throttles. The linkage is such, however, that movement ofthe primary throttles from this partially-open position to wide-opencauses full opening of the secondary throttles. Upon closing of theprimary throttles, the aforementioned spring which may be used on thesecondary throttles causes the secondary throttles to follow themovement of the primary throttles. Full closing of the primary throttlesengages shoulder 114 with lug 115 to lock the secondary throttles in aclosed position.

Of course, if the choke valve-operated lock-out mechanism previouslydescribed is in operation, the secondary throttle cannot be opened, andspring 105 will allow for movement of the primary throttles in'anopening direction after engagement of lug 107 with shoulder 113.

As shown in Figs. 2 and 3, the carburetor is provided with a fuel bowlhaving two identical float chambers 40 and 41. (A description of onewill sufiice for both.) These chambers are interconnected by arestricted passage in which is located the supply point for two fuelnozzle systems.

Float chamber 40 contains a float 42 mounted on a float control arm 43pivoted on a'shaft '44 supported by structure depending from float bowlcover 46 Finger on arm 43 engages and actuates a needle valve 47, which,in turn, controls the supply of fuel past valve seat 48 from a commoninlet 49 for both chambers 40 and 41 shown in Fig. 1. Float 42 andneedle valve 47 maintain a substantially constant fuel level within thefuel bowl 40-41.

The passage between the float chambers 40 and 41 has two meteringorifices 50 and 50' located in the lower portion thereof. Each is, inturn, controlled by metering pins 51 and 51 carried at the upper end bya cross-bar 52 shown clearly in Figs. 1 and 2. This cross-bar is formedas an integral part of a stem 53 projecting upwardly from a piston 54,Which works in a cylinder 55 connected by means of a passage 56 to theprimary mixture conduit posterior of the throttle 22. A coil spring 57constantly urges the piston and metering pins upwardly against the forceof suction acting downwardly on the piston.

Journaled in the fuel bowl cover 46 is a countershaft 58 which mounts anactuating lever 59 having a finger 60 underlying the cross-bar 52 so asto lift the cross-bar and metering pins when the countershaft isrotated. The countershaft, in turn, is connected to the primary throttlevalves by an actuating arm 61 rigid with the projecting end of thecountershaft 58 and a link 63 connected to throttle lever actuating arm27.

Also attached to the countershaft is a lever 65 which is connected by asmall link 66 to an accelerating pump piston not shown. This pistonworks in the usual cylinder and draws fuel into that cylinder on upwardmovement of the piston. Upon opening movement of the accelerator, thefuel is discharged from the cylinder of the pump past suitable checkvalves and into the primary mixture conduit through pump jets 76, all ina well known manne'r, as shown in the co-pending application to OttoHenning, Ser. No. 268,811, filed January 29, 1952. The mechanism justdescribed is mounted under a dust cap 62 as shown in Figs. 1 and 2.

The main fuel supply from each fuel bowl to adjacent primary andsecondary mixture conduits is through individual fuel nozzle systemswhich are identical. Consequently, only one fuel nozzle system will bedescribed. In Fig. 2, fuel through the metering orifice 50 is suppliedto a main fuel passage 77 through a connecting passageway. Passage 77 isinclined upwardly as shown in Fig. 4, and conencts with a fuel tube 78extending across and between inner venturi tube 79P and 79S in theprimary and secondary conduits. Tube 78 has fuel ports 80 and 81 inthese venturi tubes, respectively, and air bleed openings 82 and 83 moreor less in alignment therewith. A vertical passage 84 connects between aport 85 adjacent the secondary throttle and a restriction 86 in the fueltube 78. The main fuel system also includes a combination air bleed andvapor vent orifice 87 connecting with the inclined fuel passage 77.

Idling fuel nozzles are provided for each primary mixture conduit. Theseare identical, and a description of one will suflice for both. Thisidling system has a vertical well 90 containing an idling tube 91 whichconnects through a series of passages 92 with idling ports 93 and 94adjacent the primary throttle 22.

Operation With the primary throttle 22 in idle position and thesecondary throttles 23 closed, fuel is supplied to the separate idlenozzles in the separate primary mixture conduits from the fuel bowl 40,41 through the metering orifices 50, 50', inclined passages 77, and idletubes 91, to the idle ports 93 and 94. As the primary throttles areopened, suction gradually increases in the inner venturi tubes 79P whichproduce a flow of fuel through the fuel tubes 78, and thence to andthrough discharge nozzles 80. Simultaneously, suction decreases at theidle ports and a gradual transition takes place until nozzles 80 supplyall of the fuel. The action of suction on the fuel nozzles 80 issomewhat modulated by the leakage of air at atmospheric pressure throughthe ports 81, 82, 83 and 85 into the fuel tubes 78 when the throttles inthe secondary mixture conduits are closed. This modulating eifect of theair bleeds reduces the discharge from nozzles 80 to give a propermixture for part-throttle operation.

When the primary throttles are opened far enough to begin opening thesecondary throttles 23, then suction will exist in both the primary andsecondary inner venturis 79P and 795, which will reduce the amount ofair bleed through ports 81 and 83 and thereby increase the rate of fuelflow into the fuel tubes 78 in order to initially increase the amount offuel to the fuel nozzles 80. Further opening of the secondary throttlesincreases the suction at ports 81 and 83 to further increase the flowthrough tubes 78 to supply suflicient fuel for both the primary andsecondary nozzles. During the initial opening of the secondary throttles23, ports 85, initially wholly anterior thereto, will be graduallyexposed to manifold suction which, in turn, will decrease theeffectiveness of these air bleeds and increase the amount of fueldelivered to enrich the mixture in the primary stages. But thisinvention contemplates the use of the device with or without the ports85. The function would be the same regardless of their presence orabsence.

Another advantage besides those-which are obvious and flow directly fromthe simplification of the mechanism, resides primarily in the feature ofproviding a carburetor of this type wherein the fuel is lifted aconstant amount regardless of tip angle. In Fig. 7, for example, if thecarburetor is tipped backwards due to a steep ascent, the amount of liftnecessary to get the fuel to both the primary and secondary nozzlesremains the same, as illustrated by intersection of lines xx and nn, thelatter being the normal fuel level. This is fixed by the fact that thedistance from the fuel levels nn and x-x to the intersection of passage77 with the fuel tube 78 remains substantially constant because thecontrol point at the intersection is located vertically above andsubstantially centrally of the fuel chamber 40. Consequently, the amountof lift due to tip angle is unchanged. Because of this, the carburetorwill operate as satisfactorily at an inclination as at a level position.If the carburetor is tilted the other way (or forward, as illustrated byline y-y), the lift also remains unchanged. The secondary fuel nozzlewill be above the primary, but this would only be in descending a steepgrade, when it is very unlikely that the secondary throttle would beheld wide open and when a leaner mixture in the secondary stages isdesirable anyway.

Fig. 6 shows a modification of the invention described above in whichmetering rods are provided in each of the mixture conduits for operationwith the fuel ports in the fuel tubes. In this modification, fourmetering rods 151 are received in the fuel ports 80, 81, respectively.The rods are pivotally connected at 152 with arms 153 mounted on thethrottles 22 and 23, respectively. Metering rods 151 are provided withstepped ends 154 received in the fuel ports 80, 81, and air bleedorifices 82, 83.

In this modification, with only the primary throttles open, flow fromthe ports 80, 81 is controlled by the metering rods received therein.Because suction will exist only at the primary nozzle, the mixture isalso controlled by the amount of air admitted by the metering rods 151in the secondary nozzles through the ports 81, 83, 85. After thesecondary throttles open, suction will exist in both the primary andsecondary nozzles, and port 85 will aid in lifting the fuel from thebowl. This will increase flow sufiiciently to provide adequate fuel inboth the primary and secondary nozzles. However, this inventioncontemplates the omission of port 85.

The invention may be modified as will occur to those skilled in the artand the exclusive use of all modifications as come within the scope ofthe appended claims is contemplated.

We claim:

1. In a multi-stage carburetor, primary and secondary mixture conduits,primary and secondary throttles, respectively, controlling saidconduits, a fuel bowl, a floatoperated valve for controlling the fuelsupply to said bowl, a fuel metering orifice in the lower part of saidbowl, a main fuel passage from said orifice to a control point above thefuel level and adjacent the middle of said fuel bowl, a fuel tubeconnecting with said passage at said control point and extendingtransversely through said primary and secondary mixture conduits, andprimary and secondary fuel nozzles in said tube for the respectivemixture conduits, whereby a substantially constant relationship ismaintained between the fuel level and said control point to supply eachsaid nozzle uniformly on inclination of said carburetor.

2. The combination defined in claim 1, with fuel metering means in saidsecondary nozzle controlled by said secondary throttle.

3. The combination defined in claim 1, with fuel metering means in saidnozzles actuated by said throttles.

4. The combination defined in claim 1, with means in said secondarymixture conduit in communication with said tube to modulate the effectof suction in the primary nozzle during part-throttle operation of saidcarburetor.

' mospheric bleed.

- 5. The combination defined in claim 4, in which said means in saidsecondary mixture conduit includes an at- 6. The combination defined inclaim 5, in which said atmospheric bleed includes a port adjacent thesecondary throttle swept by opening movement of said throttle.

7. In a multi-stage carburetor, primary and secondary mixture conduits,primary and secondary throttles, respectively, controlling saidconduits, a fuel bowl, a float-operated valve for controlling the fuelsupply to said bowl, a fuel metering orifice adjacent one side of saidbowl, a main fuel passage from said orifice to a control point above thefuel level and adjacent the center of said fuel bowl, a fuel tubeconnecting with said passage at said control point and extendingtransversely through said primary and secondary mixture conduits, and afuel nozzle in said tube for each mixture conduit, whereby asubstantially constant relation is maintained between the fuel level andsaid control point to supply each said nozzle uniformly on inclinationof said carburetor.

8. The combination defined in claim 7, with fuel metering means in saidsecondary nozzle actuated by said secondary throttle.

9. The combination defined in claim 7, with fuel metering means in saidnozzles actuated by said throttles.

10. The combination defined in claim 7, with means in said secondarymixture conduit in communication with said tube to modulate the effectof suction in the primary nozzle during part-throttle operation of saidcarburetor.

11. The combination defined in claim 10, in which said means in saidsecondary mixture conduit includes an atmospheric bleed.

12. The combination defined in claim 11, in which said atmospheric bleedincludes a port adjacent the secondary throttle swept by openingmovement of said throttle.

13. In a multi-stage carburetor, primary and secondary mixture conduits,sequentially operated primary and secondary throttles for said conduits,a constant level fuel bowl, and a fuel nozzle system for said mixtureconduits comprising a plurality of fuel discharge passages connectedwith said fuel bowl and said primary mixture conduit, an idle port insaid primary passage adjacent said primary throttle, a main fuel tubeconnected with said passages and extending to said primary and then tosaid secondary mixture conduits, a fuel nozzle for said primary mixtureconduit communicating with said main fuel tube, and means to produce anenriching effect in the primary mixture conduit on initial opening ofsaid secondary throttle, including an air bleed connecting said mainfuel supply and said secondary mixture conduit at a point in a zonepressure-sensitive to throttle positions.

14. The combination of claim 13, wherein said air bleed is adjacent saidsecondary throttle.

15. The combination of claim 13, wherein said air bleed is adjacent saidfuel nozzle in said secondary mixture conduit.

16. In a multi-stage, multi-barrel carburetor, a pair of primary and apair of secondary mixture conduits, sequentially operated pairs ofthrottles for said pairs of conduits, a constant level fuel bowl, and apair of fuel nozzle systems for each pair of said mixture conduitscomprising a plurality of fuel discharge passages for each of saidnozzle systems separately connected at adjacent points with said fuelbowl and with each said primary mixture conduit, idle portscommunicating with said passages adjacent said throttles in said primarymixture conduits, a pair of main fuel tubes separately connected withsaid fuel bowl through said passages and extending to said primary andthen to said secondary mixture conduits, a fuel nozzle for each saidprimary mixture conduit communicating with each of said main fuel tubes,and means to produce an enriching effect in said primary mixtureconduits on initial opening of said throttles in said secondary mixtureconduits, including an air bleed connec'ted with "said main fuel tubesand 'said sebondary mix- Rf'ern'es Cited in the fil'e bf't'hipateiitture conduits at a "point in a zone pressure sen'sitive to UNITED STATEgp throttle positions. n I

18. The combination of claim 16-, wherein said air bleed is adjacentsaid fuel nozzle in said secondary mixture conduit.

